Back when Microsoft released CRM 2013, they introduced a new feature to allow outer joins in FetchXML . You can find more details in this blog post about Left Joins in CRM 2013. The annoying thing is that this feature has not been surfaced through the Query designer for advanced find within CRM. It’s not a big issue, as most scenarios for this type of joins are intended for reports and you don’t use the designer for that. However, I’ve come across a number of scenarios where we wanted to define Dynamic Marketing Lists with queries that required this type of functionality – e.g. accounts with no activities in the last x weeks. The good news is that you can use the APIs to manipulate the Dynamic Marketing Lists definitions and change its FetchXML programmatically. So, even if the Advanced Find designer doesn’t support outer joins, you can still modify the query programmatically and the Marketing List will function as expected.